Yi Liu created HDFS-8884:
----------------------------
Summary: Improve BlockPlacementPolicyDefault#chooseTarget to check
candidate datanode first
Key: HDFS-8884
URL: https://issues.apache.org/jira/browse/HDFS-8884
Project: Hadoop HDFS
Issue Type: Improvement
Reporter: Yi Liu
Assignee: Yi Liu
In current BlockPlacementPolicyDefault, when choosing datanode storage to place
block, we have following logic:
{code}
final DatanodeStorageInfo[] storages = DFSUtil.shuffle(
chosenNode.getStorageInfos());
int i = 0;
boolean search = true;
for (Iterator<Map.Entry<StorageType, Integer>> iter = storageTypes
.entrySet().iterator(); search && iter.hasNext(); ) {
Map.Entry<StorageType, Integer> entry = iter.next();
for (i = 0; i < storages.length; i++) {
StorageType type = entry.getKey();
final int newExcludedNodes = addIfIsGoodTarget(storages[i],
{code}
We will iterate (actually two {{for}}) all storages of the candidate datanode
even the datanode itself is not good (e.g. decommissioned, stale, too busy..),
since currently we do all the check in {{addIfIsGoodTarget}}.
We can fail-fast: check the datanode related conditions first, if the datanode
is not good, then no need to shuffle and iterate the storages. Then it's more
efficient.
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